When tungsten ores such as scheelite, wolframite, huebnerite or mixtures thereof are digested in an alkali medium, the calcium, iron, and manganese which are present in the ores are precipitated or form an insoluble material which is separated from an alkali tungstate solution by filtration. A caustic digestion process of various tungsten ores is described in U.S. Pat. No. 3,911,007. Since the ores vary in composition, this insoluble material can contain additional elements as scandium, aluminum, niobium, tin, molybdenum, magnesium, possibly sulfur and phosphorus, etc. Also because the digestion for tungsten is not always efficient, the residue can contain some tungsten. It is desirable from an economic and environmental standpoint to recover the scandium from such residues.
U.S. Pat. No. 4,624,703 relates to a process for recovering scandium, tungsten, iron, and manganese which includes a step to recover scandium from solution by extraction with a dialkyl phosphoric acid which is dissolved in an aromatic solvent. Hence this process is a liquid-liquid extraction. Such liquid-liquid extraction processing requires a heavy outlay of capital equipment and is labor intensive.
The present invention makes use of an alkyl phosphoric acid to extract scandium in a system which makes use of relatively simple equipment and is much less labor intensive. Therefore, the process is very economical compared to prior art methods.